The present invention relates generally to automotive-related specialty products, and more particularly, to a composite drain plug for use in the oil pan of an automotive engine, or for use in another application wherein a fluid is sealed within an enclosed area from which it is desired to permit periodic draining and replenishment of fluid requiring plug removal. When used as a drain plug for an automotive engine oil pan, the one-piece unit of the invention comprises a plug body and a seal arrangement having a number of design features particularly adapted to solve persistent problems in the area of drain plug sealing.
By way of background, in the automotive industry, literally millions of automotive engines are produced every year. Each of these engines is designed to operate for an extremely extended life, and according to current practice in the automotive industry, such engines are designed to operate with an absolute minimum of maintenance. At the current time, oil change intervals of 5,000 to 7,500 miles or more are not uncommon. In earlier times, oil change intervals of 1,000 to 2,000 miles were common. Accordingly, under earlier conditions, slight leakage from drain plugs was not a critical matter, inasmuch as fluid replenishment was both common and frequent.
Referring to another, more important problem, that of modern automotive design, for environmental reasons as well as for reasons of warranty coverage, virtually absolute reliability is becoming a requirement in the automotive industry. With the increased cost of automobile engines, and particularly in view of their incorporation into compact mechanisms which include front wheel drive assemblies and the like, replacement of an engine under warranty is not only highly expensive, but is also a highly labor-intensive operation. In this latter aspect, the trend to making modern mechanisms more compact in the interest of space and weight saving has further aggravated the trend toward rendering engines and their parts almost inaccessible.
Accordingly, it is of the utmost importance that an engine or like sealed and lubricated component not fail by reason of a leaky drain plug. In the automotive industry, it was at one time common to use a steel-to-soft metal interface, usually in the form of a brass or copper washer, as a part of the drain plug sealing mechanism. However, with repeated use, such washer might be lost, scored or otherwise damaged, so such an approach has not been fully satisfactory. Cost and lack of reliability are also drawbacks to the approach of separate sealing elements.
For some time, synthetic resinous materials have been used as washers in sealed applications. While there are some advantages to this approach, new automotive engines achieve constantly higher operating temperatures, at least transiently, and obtaining suitable plastic materials for sealing engine parts is difficult.
Moreover, the practice of painting engine components, as well as painting entire cars, now commonly involves processes wherein either the entire automobile or the components thereof are baked for curing purposes under considerable heat by infrared lamps or otherwise. Under these conditions, resinous materials used as a part of the sealing system may have either been inadequate to withstand high temperatures, or more commonly, the resinous material undergoes cold flow and takes a compression set, thus compromising the residual compressive force needed to maintain a seal.
Thus, a part which is initially sealed in a highly fluid-tight manner might lose its seal with the passage of time. Some such units may even lose substantial sealing effectiveness before leaving the place of manufacture.
Certain attempts have been made to provide electrometric seals for these applications, but the use of separate elastomeric washers and the like has created problems with assembly, and also has created problems of controlling the degree of compressive force which is applied as the parts are fastened together during assembly. While insufficient forces create a risk of leakage, excessive forces have been known to damage the elastomeric or plastomeric seal components and thus create a risk of leakage in the short or long term.
Referring now to another aspect of modern manufacture and quality assurance, it has always been desired to place the responsibility for the effectiveness of any one mechanism, particularly parts that create a seal, with one manufacturer so that quality can be assured and so that responsibility can be properly located. Accordingly, manufacturers almost always wish to have mating parts made by the same entity, if this can be done as a practical matter.
In view of the failure of the prior art to provide a completely satisfactory and economical oil pan sealing system, it is therefore an object of the present invention to provide an improved such product at low cost.
Another object of the invention is to provide a composite drain plug having an integral sealing element bonded thereto and adapted for highly reliable installation.
A still further object is to provide a plug design which by reason of the type of materials used limits the torque which can be applied by the user.
A still further object is to provide a drain plug having a metal threaded portion, a head portion with a stub flange made from a thermoplastic material, and an enlarged flange and gasket portion made from an overmolded thermoplastic vulcanizate.
A still further object is to provide a drain plug which includes a specially shaped metal exterior, a plastic head, an internal body and stub flange and an elastomeric seal element integrally bonded to and serving as an extension of the flange.
Another object is to provide a drain plug which includes a steel threaded sleeve along with two other components comprising the bolt head and the sealing flange.
A still further object is to provide a drain plug having a reduced cost as well as higher quality in relation to prior art drain plugs.
Yet another object is to provide a drain plug which can be made with fewer steps, owing to its manufacturing method.
A further object is to provide a drain bolt which includes a metal sleeve which requires no preparation for rust protection, and in which the bolt head portion may be made in colors, if desired.